At the beginning choose your skill level and then see a short tutorial about the game modes. Well, game is really great and very funny but there is a little bit lack of creatures. Pick the best towers and put them on the desk intersection where little pests passing by. For the beginning take low cost towers and try take down all of them. After killing few waves of pests you will earn some gold / money, use that to upgrade your towers. When enough passes waves of pets then they will passing their big boss. Try eliminating every one of them and having a lot of fun.